This invention relates to a jet aircraft provided with vectorable exhaust nozzles for directing exhaust gas from a gas turbine engine generally downwards or rearwards.
The principle of thrust vectoring using four rotatable nozzles on a bypass type gas turbine engine is well known and described in detail in UK Patent Specification Nos. 881,662 and 881,663.
To increase the operational flexibility of such an aircraft it is known to provide a gas turbine engine as described in UK Patent Specifications Nos. 1,415,679 and 1,389,347 with four vectorable nozzles. In such an arrangement the engine has two modes of flow. In a `series` mode the engine takes the form of a turbojet in which a first fan or compressor effectively supercharges the air flow into a second compressor. The total mass flow through the engine is discharged through the rear two nozzles. In some aircraft configurations the rear two nozzles may be replaced by a single fixed or vectorable nozzle.
In a `parallel` mode the engine functions as a bypass or turbofan engine in which air from the first compressor or fan is discharged through the front nozzles while a second flow is induced through a separate second intake to flow into the second compressor and thence to the combustion and turbine apparatus and finally to be discharged through the rear nozzle or nozzles.
When the engine is in the series mode the front nozzles are not in use but they can be a source of considerable drag as the aircraft will be travelling at its highest speed in this mode.
Co-pending U.S. patent application No. 849,492, filed Apr. 8, 1986, inventors G. F. Szuminski and D. J. Nightingale, discloses an aircraft in which the front nozzles are stowed in the fuselage when not in use. In this arrangement the front nozzles have three distinct positions--stowed, rotated for vertical thrust, and rotated further for horizontal thrust.
A simpler arrangement would be for the nozzle to have only two positions such that the nozzle is stowed when in the vertical thrust position.
Prior configurations have also suffered from a suck down effect when the aircraft is hovering near the ground. If this suck down effect could be reduced then the aircraft will be able to operate with greater efficiency and safety near the ground.